The present invention relates to radiocommunication systems (e.g., cellular or satellite systems), and more particularly to techniques for steering radio traffic to preferred servers (e.g., base stations) when more than one candidate server exists.
In today's advanced radio telecommunication networks, there is a growing need for the ability to differentiate between different categories of end users (e.g., subscribers). This need may arise, for example, for a number of marketing reasons. One example of a marketing-driven reason for end user differentiation would be an operator's desire to guarantee that a selected group of end users (e.g., the employees of a particular company) will experience a certain traffic capacity when within the coverage area of certain servers (e.g., when within the coverage of the server installed at the company premises). In order to make this possible, it is important that other subscribers, not belonging to this subscriber group, be prevented from causing any traffic load in those specific servers.
Another example of a marketing driven reason for end user differentiation would be an operator's desire to offer subscriptions that are allowed access to only a limited part of the operator's network. The allowed service area is defined by a geographical area having coverage from one or several radio communication servers (e.g., base stations). In this case, it is important that the mobile station not cause any load in the radio communication system when it is situated outside the allowed service area. Furthermore, it is important for the subscriber in this instance to be alerted to the fact that he/she has traveled outside the allowed service area. This should be indicated by the mobile station.
Yet another example of a marketing motivated reason for end user differentiation would be an operator's desire to offer subscriptions with different tariff classes depending on the area where the service is requested and/or is received. In this case, it is important that the mobile station have information about the user's preferred service area(s) in order to choose the most preferred service area from among the presently available service areas. In this case, it is also important to make it possible for the user to know ahead of time whether a requested service setup will be done in the preferred area or not.
Despite the desirability of end user differentiation, the existing GSM mobile station (MS) idle mode cell selection/re-selection procedure does not include any subscription area considerations within a selected Public Land Mobile Network (PLMN). At best, it is possible for a GSM network operator, using conventional techniques, to:
1) define subscriptions with allowed access in only a part of the network (e.g., a predefined subset of cells); PA1 2) limit the access of a number of subscribers (i.e., a "subscriber group") to only a part of the network (e.g., a predefined subset of cells); and PA1 3) set special tariffs and allow special services depending on the subscription and where the subscriber makes the access. PA1 1) For a subscriber with allowed access in a limited part of a PLMN (i.e., a limited part of a GSM radio network), the mobile station will nonetheless occupy radio and network resources in the PLMN even though it may be outside the allowed part. PA1 2) For a subscriber with allowed access in an entire PLMN but with preferred access in a limited part of this PLMN, the mobile station can initiate connection set-up in cells outside the preferred part of the PLMN although there is another cell, belonging to the preferred part, that is suitable. For the definition of "suitable", see the ETSI publication TS GSM 03.22, v.4.11.0, which is hereby incorporated herein by reference. PA1 3) Even if only a specific subscriber group is to be allowed access in a limited part of a PLMN, it is presently not possible to completely prevent other mobile stations (i.e., mobile stations associated with other subscribers) from occupying radio and network resources in this part of the PLMN.
However, if the network operator wants to have such functionality/service, then it must be handled by the network itself because, at present, the GSM standard does not give any support for any service area considerations during the MS idle mode cell selection. The MS does not have any subscription area information available when performing the idle mode cell selection. Consequently, the cell selection will be done in a similar way by all MSs within the PLMN, independent of the subscription.
Looking, for example, at a conventional approach to limiting a user's access to only a part of a network, when an MS has camped on a cell and is ready for service, the user is able to initiate a call set-up. Initially, this will result in a signaling connection being established up between the MS and the network. The network can then authenticate the MS and make necessary subscription controls. Depending on factors such as the subscription service area data (if any), the network can either accept or reject the call set up.
If the network rejects the call setup because the access was made outside the allowed area for the user, or if the access was made in a cell dedicated to be used only by a subscriber group to which the user does not belong, the signaling connection will be released. However, in the conventional systems, it is not possible for the network to prevent the user (i.e., the MS) from making a retry in the same cell. Such a retry will again result in a rejection from the network. It can be seen that the use of conventional techniques to introduce this type of end user differentiation functionality detrimentally loads the radio and network resources.
A further consequence of the conventional approach to defining a restricted coverage area for a user will be appreciated by considering an example in which an MS is in the coverage area of two cells, here designated cells A and B, each of which is suitable to camp on. Suppose that the MS calculates the C1 criterion for each of cells A and B, and finds that cell A is the best call and camps on this cell. If the user's subscription data indicates that only cell B is allowed to be used, the user's attempt to initiate a call will be rejected by the network (i.e., because the user has attempted a call through cell A). However, the conventional techniques do not provide any mechanism for either the user or the network to force the MS to camp on the other cell (i.e., cell B). Consequently, if radio conditions remain the same (e.g., the user does not move), the MS will continue to camp on cell A, and subsequent attempts to establish a call will all be futile.
Consider now an example in which conventional technology and techniques are applied to implement a "preferred area", that is, the designation of some cells in the system as being preferred over other cells with respect to handling calls initiated by a particular subscriber's MS. For this illustration, assume that the MS is in the coverage area of two cells (designated cell A and cell B), each of which is suitable to camp on. Assume further that the MS calculates the C1 criterion for each of cells A and B, and finds that cell A is the best cell. This would cause the MS to camp on cell A.
Suppose, however, that this subscriber's subscription data indicates that cell B is preferable to cell A (e.g., suppose that this subscriber's use of cell B will be free of charge, and that use of cell A will not be). Under these circumstances, it would be desirable for the subscriber's MS to camp on cell B instead of cell A. However, so long as the radio conditions remain the same (e.g., the user does not move), the MS will continue to camp on cell A, and any call that is made will be set up in the "expensive" cell. The conventional approach simply has no way to force the MS to camp on the other cell.
To recapitulate,
Conventional systems fail to provide a satisfactory solution to these problems. For example, International Patent Application No. WO 95/07010 discloses a communication system in which a mobile station can switch between available domains in areas of overlapping coverage. The selection of domains is made on the basis of which services are to used. However, this publication fails to disclose any techniques for distinguishing between allowed domains, disallowed domains, respective preferred domains for camping and registration of a mobile network subscriber on the basis of subscriber identity irrespective of service.
U.S. Pat. No. 5,627,877 discloses an adaptive relocation of subscriber data between network entities when the subscriber moves in order to reduce demand for intra-network traffic. This publication does not disclose the possibility of reducing network traffic by defining allowed/disallowed service areas that are distinguished from one another, in the cell selection process performed by the mobile station, on the basis of subscription data.
U.S. Pat. No. 5,404,580 discloses the possibility of a particular radio telephone (i.e., particular mobile equipment) that only works with a particular Subscription Identification Module (SIM). This is effected by incorporating a memory unit into the radio telephone itself, wherein the memory unit has stored therein some subscription data. The obtained services are then dependent on the combination of this memory unit data and the SIM card that has been inserted into the radio telephone. U.S. Pat. No. 5,444,764 discloses a special case for the functionality given by U.S. Pat. No. 5,404,580. This special case gives the possibility of restricting the usage of a particular radio telephone to a subscriber with a SIM that has an IMSI that falls within a range of valid IMSIs. Information about these valid IMSIs is programmed into the radio telephone's own memory module.
U.S. Pat. No. 5,499,386, discloses a multi-level layered cellular radio architecture that serves mobile subscriber stations moving within the system. Best server selection is performed for the mobile stations by assigning within each cell a preference value to each other one of the cells with which it is associated by proximity of service area. The strength of the radio signal received by the mobile from the serving cell as well as the radio channels of associated cells is measured. A decision as to the best serving cell for the mobile station is made based upon both the preference value of the associated cells and the signal strength of their respective radio channels. In this manner, a Hierarchical Cell Structure (HCS) is established. However, the parameters that determine preferences in the cell selection process are the same for all mobile stations regardless of subscription.